The present invention relates to a method for forming coating films such as a transparent electrical conductive film and reflective film on a substrate surface, more specifically, a coating film forming method and device by which evenness in coating film thickness is increased.
A method has been conventionally used in which substrates are attached to the inside surface or outside surface of a rotatable drum-shaped substrate holder, and coating film material particles are evaporated from a coating film material placed at a position opposite to the substrates while rotating the substrate holder, whereby coating films are formed on the substrate surfaces. As a method for forming coating films, vacuum evaporation method and sputtering method have been generally used.
FIG. 6 is a schematic view showing an example of such a vacuum evaporation device. In the vacuum evaporation device shown in FIG. 6, a plurality of substrates 2 are attached to the inner wall surface of a rotatable drum-shaped substrate holder 1, and while rotating the substrate holder 1, that is, while revolving the substrates 2, coating film material particles are evaporated from a coating film material (hereinafter, referred to as evaporating source 3) located at the revolution central position of the substrate holder 1, whereby coating films are formed on the surfaces of the substrates 2.
FIG. 7 is a partial sectional view showing disposition of the substrates and substrate holder of the vacuum evaporation device shown in FIG. 6.
Recently, formation of a coating film on a substrate having a great area has been demanded, on the other hand, uses of coating films have increased in which evenness in coating film thickness across the entire surface of the substrate with a great area is demanded. For example, such a technique achieving this is increasingly expected in uses for an electrical conductive film coated substrate, reflection preventive film coated substrate, reflective film coated substrate, a semi-transparent film coated substrate, electromagnetic shielding film coated substrate, and infrared ray shielding film coated substrate. Furthermore, these film-coated substrates are used for various displays including a liquid crystal display (LCD), organic electro luminescence (EL) display, and plasma display panel (PDP), and in addition, used for architectural members and vehicle members.
A film thickness is determined in accordance with the density on the substrate surface of coating film material particles reaching the substrate surface from the evaporating source within a unit time. The density on the substrate surface of the coating film material particles depends on the angle of inclination of the normal direction of the evaporating source surface with respect to the straight line linking the evaporating source and a specific position of the substrate surface, and depends on the distance between the evaporating source and substrate surface.
When it is assumed that the normal direction of the evaporating source surface is a solid angle of xcfx86=zero degrees, the density of coating film material particles which is evaporated in the direction of the solid angle xcfx86 follows the so-called cosine rule, and is in proportion to the n-power (n≈1 to 3) of cos xcfx86.
The density of the coating film material particles to be evaporated is in inverse proportion to almost the square of the distance from the evaporating source. For example, the relationship of the density of the evaporated particles between point (a) with a d1 distance from the evaporating source and point (b) with a d2 distance from the evaporating source is roughly as follows:
density of evaporated particles at point (b)xe2x88x9d
density of evaporated particles at point (a)/(d2/d1)2 
That is, the more distant from the evaporating source, the smaller the density of evaporated particles reaching the substrate. As a result, the film thickness on the substrate surface at a distant position from the evaporating source becomes thinner than that at a position close to the evaporating source.
In order to form a coating film thickness which is even across the entire substrate surface, a film thickness correcting plate has been conventionally provided between the evaporating source and substrate. The film thickness correcting plate has a function for making the film thickness even across the entire substrate surface by eliminating density differences of evaporated particles reaching the substrate caused by the solid angle from the evaporating source and/or the distance from the evaporating source and substrate and making the density even.
FIG. 6 shows a film thickness correcting plate 5 provided for improving the film thickness distribution in the direction orthogonal to the direction of revolution of the substrates 2 disposed on the inner wall surface of the drum-shaped substrate holder 1. The film thickness correcting plate is shaped so that, for example, as shown in the plan view of the film thickness correcting plate 5 of FIG. 8, the width is changed along the direction orthogonal to the direction of revolution of the substrates 2.
In the evaporation method using the vacuum evaporation device shown in FIG. 6, when the film thickness correcting plate 5 is not provided, a film thickness distribution is obtained in which the film thickness of a coating film formed at the position on the substrate surface at which the solid angle xcfx86 from the evaporating source 3 is great and the distance between the evaporating source 3 and substrate 2 is long becomes thinner than the thickness at a position on the substrate surface at which the solid angle xcfx86 from the evaporating source 3 is small and the distance between the evaporating source 3 and substrate 2 is short.
Since the film thickness correcting plate 5 shown in FIG. 8 is shaped so that the width decreases toward both ends, the number of evaporated particles shielded at the x portions at both ends is smaller than that shielded at the central y portion, so that the film thickness distribution of the coating films on the surfaces of the substrates 2 can compensate a deviation in the film thickness distribution occurring in the case where the abovementioned film thickness correcting plate is not provided.
In the Japanese Unexamined Patent Publication No. H11-061384, a evaporation method for forming coating films on the surfaces of the substrates 2 by using a vacuum evaporation device while revolving the substrates 2 is disclosed, and in said evaporation method, in order to make the film thickness on the surface of the substrate 2 even, for example, a film thickness correcting plate 6a roughly shaped into a polygon as shown in FIG. 11(a) and a film thickness correcting plate 6b shaped into a triangle plane as shown in FIG. 11(b) are used. In this publication, the substrates 2 are disposed so that the distances between the substrate 2 and the evaporating sources 3a and 3b are greatly different from each other at the entire surface of the substrate 2, so that the shapes of the film thickness correcting plates 6a and 6b and a disposition method for the plates to compensate the film thickness distribution due to the difference between the distances from the evaporating sources 3a and 3b are described.
However, in a method in which a coating film is formed while revolving the substrates 2 by means of the vacuum evaporation method, the film thickness correcting plates 5, 6a, and 6b used in the prior arts can improve a deviation in the film thickness distribution in the direction orthogonal to the direction of revolution of the substrates 2, however, these cannot improve a deviation in the film thickness distribution occurring in the direction of revolution of the substrates 2.
A deviation in the film thickness distribution due to the difference in the solid angle xcfx86 from the evaporating source 3 does not occur in the direction of revolution of the substrates 2. The time average of the solid angle xcfx86 between each position in the direction of revolution within the substrate surface and the evaporating source 3 becomes fixed at any position in the direction of revolution since the substrates 2 revolve.
However, there is a case where a deviation in the film thickness distribution occurs in the direction of revolution of the substrates 2 due to different distances from the evaporating source 3 although the solid angle xcfx86 is fixed, and such a deviation in the film thickness distribution cannot be solved by the prior arts in principle. The reason for occurrence of a deviation in the film thickness distribution in the direction of revolution of the substrates 2 due to a difference in distance from the evaporating source 3 even in a case of a constant solid angle xcfx86 is explained with reference to FIG. 9.
When one substrate 2 revolves in the direction of the arrow A in the figure, even when the solid angle xcfx86 from the evaporating source 3 is constant, the end (point (b)) of the substrate 2 in the direction of revolution and the center point (point (a)) of the substrate 2 in the direction of revolution are different in distance from the evaporating source 3. That is, point (a) and point (b) on the surface of one substrate 2 are always different in distance from the evaporating source 3 regardless of the solid angle xcfx86.
Since the point (b) is always more distant from the evaporating source 3 than point (a), the thickness at point (b) is thinner than that at point (a). Therefore, in the film thickness distribution in the direction of revolution of the substrate 2, the thickness at the center portion of the substrate 2 is thick, and the thickness at the end portion is thin.
An object of the invention is to improve a deviation in the film thickness distribution occurring in the rotation direction such as the direction of revolution of the substrate in the abovementioned method for forming a coating film.
The abovementioned object of the invention is solved by the following constitution.
(1) A method for forming coating films, in which an evaporating source is provided at a predetermined distance from one or more substrates, and a coating film material from the evaporating source is applied on the substrate surfaces while revolving the substrates around the evaporating source, wherein coating films are formed on the substrate surfaces in a condition where the radius of curvature of the substrates obtained by bending the substrates within the elasticity range is almost equal to the radius of revolution of the substrates which rotate the substrates around the evaporating source.
The evaporating source may be disposed at a center of revolution of the substrates or in the vicinity of a center of the revolution of the substrates. The evaporating source also may be disposed at positions other than a center of revolution of the substrates or in the vicinity of a center of revolution of the substrates.
Although the evaporating source is generally disposed at the center of revolution of the substrate, even when the evaporating source is not disposed at the center of revolution, this does not influence the effects of the invention. When the evaporating source is not disposed at the center of revolution, as a matter of course, distances from the respective positions in the direction of revolution within the substrate to the evaporating source are different in the condition that the substrate is at rest, however, since the substrate revolves in this invention, the time average of the distance becomes constant at positions within the substrate in the direction of revolution.
The method using the evaporation material to evaporate the coating film material by heating under reduced pressure (the vacuum evaporation method) and the method using the target to evaporate the coating film material by the sputtering (the sputtering method) may be useful in the evaporating source.
(2) A method for forming coating films, in which coating film materials from an evaporating source is provided outside of one or more substrates, and coating film materials from the evaporating source are coated on the substrate surfaces while said one or more substrates are rotated.
In this case, the method using the evaporation material to evaporate the coating film material by heating under reduced pressure (the vacuum evaporation method) and the method using the target to evaporate the coating film material by the sputtering (the sputtering method) may also be useful in the evaporating source.
(3) A coating film forming device having an evaporating source arranged section for evaporating a coating film material, and a cylindrical substrate holder which holds one or more substrates to be coated with the coating film material from the evaporating source on the wall of the holder and revolves around the evaporating source arranged section and is disposed at a predetermined distance from evaporating source arranged section, wherein the radius of curvature of the substrates is almost equal to the radius of curvature of the wall surface on which the substrates of the cylindrical substrate holder are provided.
The material of the substrate holder may be selected by considering properties such as proper heat resistance, rigidity, less dust emission, and free from emission of gases within the vacuum device. Various kinds of metal materials such as stainless steel and aluminum are generally used.
A trim-shaped presser plate which is put and fixed the substrates together with the wall surface of the substrate holder, and has a radius of curvature that is almost equal to that of the substrates may be provided.
A protective sheet with hardness smaller than that of the substrate is deposited between the substrates and the wall surface of the substrate holder, and a trim-shaped protective sheet with hardness smaller than that of the substrates may be disposed between the substrate and the trim-shaped presser plate of the substrates.
The protective sheet and the trim-shaped protective sheet may be plastics.
Since the protective sheets prevent direct contact between the substrates and substrate holder, occurrence of flaws on the substrates can be prevented, and since the protective sheets have hardness smaller than that of the substrates, the protective sheets do not damage the substrates.
A coating film forming device according to the above-mentioned (3) is the device such that one or more substrates are provided on inner wall surface of the cylindrical substrate holder which rotates around rotation axis, and the evaporating source arranged section to evaporate the coating film material are provided at the cylindrical axis of substrate holder or in the vicinity of the cylindrical axis of substrate holder, or one or more substrates are provided on inner wall surface of the cylindrical substrate holder which rotates around rotation axis, and evaporating source arranged section to evaporate the coating film material are provided at positions other than the cylindrical axis of substrate holder or in the vicinity of the cylindrical axis of substrate holder.
(4) A coating film forming device having a rotational cylindrical substrate holder which holds one or more substrates at the outside wall surface, and the other cylindrical tube having the same rotational axis with the cylindrical substrate holder and larger rotational radius than the cylindrical radius of the substrate holder and an evaporating source arranged section to evaporate the coating film material at the inner surface are provided.
According to the invention, the radius of curvature of the substrates are almost equal to the radius of curvature of the wall surface of the cylindrical substrate holder on which the substrates are disposed, whereby the film thickness in the direction of substrate revolution from the evaporating source disposed at a predetermined distance from the rotating substrates becomes even.
In the invention, coating films are formed in a condition where the substrates are bent within the elasticity range, and thereafter, the substrates are restored to be plane. Internal stresses of the coating films obtained by the method of the invention are considered as follows.
In an embodiment of the invention, a stress inside the coating film caused by restoring the coating films that have been formed in a condition where the substrates 2 are bent to be plane is calculated as approximately 35 MPa (tension) based on the elasticity theory.
On the other hand, when the formed coating films are cooled to a normal temperature in a condition where the substrates 2 are heated, a stress inside the coating films caused by a difference between the thermal expansion coefficient of the glass substrate and thermal expansion coefficient of the coating films (for example, in the embodiment described later, the average thermal expansion coefficient of SiO2 and TiO2) is calculated as approximately 150 MPa (compression) based on the elasticity theory. This internal stress at the same level also occurs in the prior arts.
Furthermore, a stress inside the coating films caused by anisotropic distortion of the crystal lattice of the coating films on the substrates 2 is calculated as 200 through 1000 MPa (compression). This internal stress at the same level also occurs in the prior arts.
Thus, an internal stress of coating films caused by the method of the invention is approximately one digit smaller than that caused by anisotropic distortion of the crystal lattice of coating films in the prior arts, so that the level of the internal stress caused by the method of the invention does not need to be considered in practical use.